1. Field of the Invention
The present invention relates to a document reading apparatus, such as an automatic document feeder (ADF) unit, and an image forming apparatus such as a copying machine and a laser beam printer provided with the ADF unit.
2. Description of the Related Art
With a conventional image forming apparatus of this type, a document conveyance path for conveying a document to a document reading unit, and a recording material conveyance path for conveying a recording material to an image forming unit are configured independently of each other. More specifically, a sheet feed unit, guide members forming a predetermined conveyance path, a plurality of conveyance rollers, a motor for driving conveyance rollers, and a sheet discharge unit are disposed separately for each of a document and a recording material.
For this reason, it is difficult for the image forming apparatus to avoid the increase in complexity of the overall mechanical configuration, the increase in cost, and the increase in size. To solve these problems, for example, Japanese Patent Application Laid-Open No. 2000-185881 discusses a technique for simplifying the configuration and reducing cost and size by using a document conveyance path and a recording material conveyance path as common conveyance paths. A document reading unit is disposed in the recording material conveyance path ranging from a sheet feed unit to a sheet discharge unit.
However, in an image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2000-185881, the document reading unit is disposed in the recording material conveyance path, for example, between a fixing device and the sheet discharge unit. Therefore, there has been a problem that, during a document reading operation during which a document exists in the recording material conveyance path, the printing operation for a recording material is suspended, resulting in degraded productivity of the image forming apparatus.
Further, in a case where a plurality of document sheets is read and printed on a plurality of recording materials with the configuration discussed in Japanese Patent Application Laid-Open No. 2000-185881, alternately performing the document reading operation and the printing operation will degrade the productivity of recording material printing because of the above-described reason. To avoid this problem, the document reading operation may be performed for all of document sheets prior to the printing operation for recording materials. In this case, however, sufficient printing productivity cannot be obtained. Further, a high-capacity image memory is required to store all of image data after the document reading operation, resulting in a cost increase.